Encapsulated tracers and chemicals for reservoir interrogation and manipulation

ABSTRACT

An apparatus, method, and system of reservoir interrogation. A tracer is encapsulating in a receptacle. The receptacle containing the tracer is injected into the reservoir. The tracer is analyzed for reservoir interrogation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 61/507,044 filed Jul. 12, 2011entitled “Encapsulated Tracers for Reservoir Interrogation,” thedisclosure of which is hereby incorporated by reference in its entiretyfor all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No. DE-AC52-07NA27344 between the United States Department ofEnergy and Lawrence Livermore National Security, LLC for the operationof Lawrence Livermore National Laboratory.

BACKGROUND

1. Field of Endeavor

The present invention relates to reservoir interrogation and moreparticularly to encapsulated tracers for reservoir interrogation.

2. State of Technology

U.S. Pat. No. 4,555,488 for tracer chemicals for a method fordetermining flow patterns in subterranean petroleum and mineralcontaining formations using organonitrogen tracers provides the state oftechnology information reproduced below. The disclosure of U.S. Pat. No.4,555,488 is incorporated herein in its entirety for all purposes.

In recovery of petroleum or minerals from subterranean formations,especially by chemical flooding, it is desirable to know the flowpatterns of the formation prior to injection of chemicals. Tracers areused in such reservoir engineering. In the actual recovery process,during chemical injections, it is advantageous to follow the flow ofeach slug by using a tracer in the slug. Ideally, a tracer should bewater soluble and inert to the solids and liquids in the formation. Byinert is meant that it does not get absorbed onto the rocks; it does notpartition into any oil phase which may be present; and it does notinteract with the organics and minerals present in the formations. Wheninjected with another chemical agent, it should also be inert to thechemical it is injected with. A tracer should also be easily andaccurately detected by simple methods without interference by anysubstances present in the connate fluids.

The tracers now employed are radioactive isotopes and compounds likepotassium iodide, ammonium thiocyanate and dichromate. Radioactiveisotopes are expensive and require special handling by licensedpersonnel. Potassium iodide and alike are detected by wet analyses and,therefore, bear the limitations of such analyses.

U.S. Pat. No. 5,246,860 for tracer chemicals for use in monitoringsubterranean fluids provides the state of technology informationreproduced below. The disclosure of U.S. Pat. No. 5,246,860 isincorporated herein in its entirety for all purposes.

In most production reservoirs, the produced brines are injected into theformation for purposes of maintaining reservoir pressure and avoidingsubsidence and environmental pollution. In the case of geothermalfields, the brines are also injected to recharge the formation. However,the injected brines can adversely affect the fluids produced from thereservoir. For example, in geothermal fields, the injected brine canlower the temperature of the produced fluids by mixing with the hotterformation fluids. In order to mitigate this problem, the subsurfacepaths of the injected fluids must be known.

Tracers have been used to label fluids in order to track fluid movementand monitor chemical changes of the injected fluid. Despite theirimportance to the reservoir operator, very few tracers are presentlyavailable. Furthermore, of those that are available, little is knownabout their stabilities or behavior at the elevated temperatures thattypify geothermal resources capable of electric power generation.

Radioactive materials are one class of commonly used tracers. Thesetracers have several drawbacks. One drawback is that they requirespecial handling because of the danger posed to personnel and theenvironment. Another drawback is the alteration by the radioactivematerials of the natural isotope ratio indigenous to thereservoir—thereby interfering with scientific analysis of the reservoirfluid characteristics. In addition, the half life of radioactive tracerstends to be either too long or too short for practical use.

United States Patent Application 2010/0307745 for the use ofencapsulated tracers provides the state of technology informationreproduced below. The disclosure of United States Patent Application2010/0307745 is incorporated herein in its entirety for all purposes.

The use of tracers to obtain information about an oil reservoir and/orabout what is taking place therein has been practiced for severaldecades and has been described in numerous documents. Primarily tracershave been used to monitor fluid paths and velocities. More than onetracer substance may be used concurrently. For instance U.S. Pat. No.5,892,147 discloses a procedure in which pluralities of different tracersubstances are placed at respective locations along the length of a wellpenetrating a reservoir. The tracer substances are placed at theselocations during completion of the well before production begins. Thetracer at each location is either attached to a section of pipe beforeit is placed at that location or is delivered into the location whilstperforating casing at that location. When production begins, monitoringthe proportions of the individual tracers in the oil or gas produced bythe well permits calculation of the proportions of oil or gas beingproduced from different zones of the reservoir.

Distinctive chemicals which can be detected in high dilution, such asfluorocarbons, dyes or fluorescers have been used as tracers.Genetically coded material has been proposed (and WO2007/132137 gives amethod for detection of biological tags). Radio-isotopes have frequentlybeen used as tracers. Society of Petroleum Engineers paper SPE109,969discloses the use of materials which can be activated to become shortlived radio-isotopes.

Hydraulic fracturing is a well-established technique for stimulatingproduction from a hydrocarbon reservoir. Typically a thickened, viscousfracturing fluid is pumped into the reservoir formation through awellbore and fractures the formation. Thickened fluid is then also usedto carry a particulate proppant into the fracture. The fracturing fluidis subsequently pumped out and hydrocarbon production is resumed. As thefracturing fluid encounters the porous reservoir formation a filtercakeof solids from the fracturing fluid builds up on the surface of the rockconstituting the formation. After fracturing has taken place a breaker(which is usually an oxidizing agent, an acid or an enzyme) may beintroduced to break down this filter cake and/or to reduce the viscosityof the fluid in the fracture and allow it to be pumped out moreeffectively.

Tracers have been used in connection with hydraulic fracturing, mainlyto provide information on the location and orientation of the fracture,as for instance in SPE 36675 and U.S. Pat. No. 3,987,850. U.S. Pat. No.3,796,883 describes a further use of radio-active tracers to monitor thefunctioning of a well gravel pack.

It is known to associate tracers with a carrier material as particlesfrom which the tracer is released after those particles are placedwithin a subterranean reservoir. For instance U.S. Pat. No. 6,723,683uses starch particles as a carrier for a variety of oilfield chemicalsincluding tracers. Association of a tracer substance with a carrier isalso disclosed in U.S. Pat. No. 7,032,662 and U.S. Pat. No. 7,347,260.

U.S. Pat. No. 6,645,769 proposes that multiple tracers should be locatedat respective zones of a reservoir during completion of a well and alsoproposes that individual tracers should be associated with carrierparticles from which the tracers are eventually released into thereservoir and hence into fluid produced from the well. This documentteaches that placing of tracers at an individual location duringcompletion of the well may be achieved by immobilization on a filter orcasing before that filter or section of casing is inserted into thewell.

United States Patent Application 2010/0307744 for the use ofencapsulated chemical during fracturing provides the state of technologyinformation reproduced below. The disclosure of United States PatentApplication 2010/0307744 is incorporated herein in its entirety for allpurposes.

It is well-known to deliver so-called oilfield chemicals (using thiscommon term to include chemicals used in connection with either naturalgas or oil and to include biochemicals such as nucleic acids andenzymes) to a subterranean hydrocarbon reservoir to bring about avariety of functions at various stages of hydrocarbon production.Methods for delivering oilfield chemicals to a reservoir include methodsin which the chemical is made into the form of particles which aresuspended in the fluid which is pumped down a wellbore to the reservoir.Common methods for forming particles are absorption into the pores ofporous carrier particles and encapsulation as a core-shell structure inwhich a single quantity (the core) of the oilfield chemical is enclosedwithin a shell of carrier material.

Hydraulic fracturing is a well-established technique for stimulatingproduction from a hydrocarbon reservoir. In a conventional fracturingprocedure a thickened aqueous fracturing fluid is pumped into thereservoir formation through a wellbore and opens a fracture in theformation. Thickened fluid is then also used to carry a particulateproppant into the fracture. Once the fracture has been made and packedwith proppant, pumping is stopped. The formation closes onto theproppant pack and oil or gas can flow through the proppant pack to thewellbore. At least some of the aqueous fracturing fluid in the wellborewill be driven back to the surface by fluid produced from the reservoir.Thickener which increases the viscosity of the fracturing fluid may be apolysaccharide. Guar gum, often crosslinked with borate or a zirconiumcompound is frequently used. Another category of thickeners which isused is viscoelastic surfactants. An oilfield chemical may be deliveredto a reservoir during fracturing. If the fracturing fluid contains aviscosifying thickener, it is normal to supply a so-called breaker(which is usually a chemical or an enzyme) into the fracture to degradethe thickener and so reduce the viscosity of the fluid in the fractureafter it has served its purpose. This facilitates the flow back to thesurface and the flow of produced fluid through the proppant pack towardsthe wellbore.

U.S. Pat. No. 4,506,734 teaches the encapsulation of a breaker chemical,which may be an enzyme, within particles which are crushed by thefracture when pumping ceases and the fracture is allowed to close ontothe proppant pack. This of course delays release of the breaker chemicaluntil the fracture formation is complete.

U.S. Pat. No. 5,437,331 discloses an encapsulated enzyme breaker formedby a procedure in which porous beads of polymer are made and exposed toa solution of the enzyme which is absorbed into the open pores of thepolymer beads. Examples in the document showed that this delayed releaseof the enzyme compared to incorporating enzyme solution directly into amodel fracturing fluid.

Proposals for encapsulation of oilfield chemicals in contexts other thanhydraulic fracturing include U.S. Pat. No. 6,818,594 which teaches theuse of enzymes which are enclosed within a polymer capsule as a breakerfor filtercake formed while drilling a well.

International Publication No. WO 03/106809 teaches particles in which anoilfield chemical (in the form of small droplets of aqueous solution) isenclosed in a matrix of an encapsulating polymer. This polymer is chosenso as to be soluble or otherwise degradable under conditions which areencountered within the reservoir after mixing with formation fluid foundin the reservoir. The document teaches that these encapsulated particlesshould be made so small (mean particle diameter below 10 micron) thatthey can enter the pores of formation rock. Although delivery ofparticles to a reservoir via a production well is mentioned, analternative possibility which is suggested is that particles can bedelivered to the reservoir via an injection well and then flow throughthe formation to the vicinity of a production well to release theencapsulated chemical (a scale inhibitor) in the near wellbore region ofthe production well. This indicates that release of the encapsulatedchemical will be sufficiently slow to allow time for travel through theformation from the injection well to the production well.

U.S. Pat. Nos. 4,506,734, 5,437,331, 6,818,594, 7,032,662, 7,347,260 andInternational Publication No. WO 03/106809 describes the variousapparatuses, methods, and systems for encapsulating materials for use insubterranean formations. The disclosures of the above noted U.S. Pat.Nos. 4,506,734, 5,437,331, 6,818,594, 7,032,662, 7,347,260 andInternational Publication No. WO 03/106809, are incorporated herein intheir entirety for all purposes.

SUMMARY

Features and advantages of the present invention will become apparentfrom the following description. Applicants are providing thisdescription, which includes drawings and examples of specificembodiments, to give a broad representation of the invention. Variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art from this descriptionand by practice of the invention. The scope of the invention is notintended to be limited to the particular forms disclosed and theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

Definition

The following term used in this patent application has the meaningdescribed below:

Tracer—Tracer as used in this application means a chemical which whenadded to a rock system may he used to infer the structure, flow rates,or chemistry and phase content of that system. The tracer may havedefined chemical interactions with the contents of the reservoir, suchas dissolving in petroleum or dissolving scale within the reservoir, orit may have very limited or zero interactions so as to maximize physicalunderstanding of the shape, length, and velocity of flow pathways ratherthan the chemistry of those pathways. Tracers can typically be detectedby recovering some of the tracer material at another point in theformation after movement through the formation, but in the usage of thisapplication, tracers can also be detected by their effect on theformation, such that a reservoir property changes in a measurable way soas to make it possible to detect where the tracer has traveled, and/orthe extent of its interaction with the formation.

The present invention provides an apparatus, method, and system ofreservoir interrogation. A tracer is encapsulated in a receptacle. Thereceptacle containing the tracer is injected into the reservoir. Thetracer is analyzed for reservoir interrogation. In one embodiment thepresent invention provides a reservoir interrogation apparatuscomprising a tracer encapsulated in a receptacle. In one embodiment thereceptacle changes chemical constituent or color or fluorescence at apredetermined temperature range or a predetermined condition. In oneembodiment the tracer will be released from the receptacle in thereservoir upon pre-determined conditions and an analysis made regardingthe collected tracer for reservoir interrogation. In one embodiment thereceptacle containing the tracer is collected after being injected intothe reservoir and analyzed for reservoir interrogation. In oneembodiment multiple tracers are contained in a capsule with multipleconcentric shells. The outer shell releases the tracer at thepredetermined condition; the second tracer is released at a secondpredetermined condition. Collection of specific tracers providesinformation on reservoir conditions and flow pathways within thereservoir. In one embodiment a capsule contains a tracer and a second orthird encapsulated distinct tracer (FIG. 14). The outer shell releasesthe first tracer at the predetermined condition; the additional tracersare still encapsulated. The second and third tracers are only releasedwhen a predetermined condition is encountered during flow through thereservoir. Collection of specific tracers at extraction wells providesinformation on reservoir conditions and flow pathways within thereservoir. In one embodiment numerous distinct tracers each of which isencapsulated in spheres that will release the tracers at specific,distinct predetermined conditions. The design of the shells and thedistinct tracers enables interrogation of reservoir conditions and flowpathways by sampling and testing fluid from extraction wells anddetermining the ratios of released and unreleased tracers. In this waythe portions of the reservoir that the flow paths sample and theconditions of the reservoir can be determined. In one embodiment therelease of the tracer is controlled by the thickness of theencapsulating wall. In one embodiment the release of the tracer iscontrolled by the composition of the encapsulating wall.

The release of tracer chemical into the formation may be furthercontrolled by the use of a dual outer shell, where one shell providesmechanical strength but is permeable to the tracer chemical held inside,and the second is impermeable to the tracer chemical but changespermeability dramatically upon achievement of a certain condition, suchas temperature, the presence of petroleum, or the presence of areservoir treating chemical like acid. In FIG. 13; for instance, 1308may be a silicone shell with high permeability to water and unchargedchemicals, and 1306 may be a polymer whose glass transition temperatureis equal to some temperature at which we wish to interrogate thereservoir. The tracer chemical 1302 is held inside the double shelluntil the temperature is reached, at which time both shells becomepermeable. This is a preferred method for dealing with situations wherethe polymer whose properties change at the reservoir condition ofinterest, such as temperature, is not strong enough on its own tosurvive transport into the reservoir. This ensures minimal leakage oftracer from capsules that break during handling as well.

Additional improvements may be made. For instance, 1304 may be anadditional polymer layer reactive to a second stimulus, requiring twostimuli to be present in order for the release of the tracer chemical.Or 1304 may be a reactive chemical or catalyst which ensures that areaction occurs between reservoir chemicals, and the tracer chemicalcontained inside, such that a transformed tracer signal is released fromthe capsule.

The release of chemical from the encapsulated system may be triggered byreservoir conditions, or it may be triggered by a stimulus applied bythe operator, such as an electromagnetic pulse, shock wave, or secondinjected chemical such as acid. In this way the encapsulated tracer maybe released in a time-oriented pulse that transmits information aboutwhere the tracer capsules were at the time of the stimulus, providing acapability to map both their ingress to the formation, and the egress ofreleased tracer after the unitary stimulus. One way to achieve thisrelease is to compose the capsule in FIG. 13 as follows: 1306 is thetracer chemical, and 1302 is an explosive material that can be detonatedby a shock wave, breaking the capsule and also transmitting the shockwave further into the formation.

Uses of the present invention include interrogation of subsurfacereservoirs where information about conditions of the reservoir isneeded. Uses of the present invention include applications thatcurrently use conventional tracer techniques.

The invention is susceptible to modifications and alternative forms.Specific embodiments are shown by way of example. It is to be understoodthat the invention is notlimited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate specific embodiments of theinvention and, together with the general description of the inventiongiven above, and the detailed description of the specific embodiments,serve to explain the principles of the invention.

FIG. 1 is a flow chart illustrating a system of the present invention.

FIG. 2 illustrates an individual encapsulated tracer.

FIG. 3 is a flow chart illustrating an example of the invention whereinthe tracer is released into the reservoir.

FIG. 4 is a flow chart illustrating an example of the invention whereinthe encapsulated tracer remains intact as it passes through thereservoir.

FIGS. 5A and 5B illustrate an example of the invention wherein anexample of the invention wherein the tracer is released into thereservoir.

FIGS. 6, 7, and 8 illustrate an example of the invention wherein theencapsulated tracer remains intact as it passes through the reservoir.

FIG. 9 is an example of the invention wherein the tracer is releasedinto the reservoir at a predetermined time.

FIG. 10 is an example of the invention wherein the tracer is releasedinto the reservoir at a predetermined temperature.

FIG. 11 is an example of the invention wherein the tracer is releasedinto the reservoir at a predetermined pressure.

FIG. 12 is an example of the invention wherein the tracer is releasedinto the reservoir at a predetermined chemical condition.

FIG. 13 is an example of the invention wherein two tracers are containedin concentric spheres where the release conditions of each tracer aredifferent.

FIG. 14 is an example of the invention wherein multiple spheres ofdistinct tracers are contained in a single sphere.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring to the drawings, to the following detailed description, and toincorporated materials, detailed information about the invention isprovided including the description of specific embodiments. The detaileddescription serves to explain the principles of the invention. Theinvention is susceptible to modifications and alternative forms. Theinvention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

A common need in geologic reservoirs is information regarding the flowpaths, temperature, pressure, and fluid characteristics of thereservoir. This information enables better extraction and management ofthe resource. Tracers tests are a standard method for obtaininginformation about the interconnectedness of individual wells, pathways,sweep efficiency, reservoir storage volume, and the types of fluid atdepth (through the use of tracers that have distinct distributioncoefficients). Subterranean fluids whose movements are capable of beingmonitored by these tracers include, but are not limited to, geothermalbrine, crude oil, ground water, hazardous waste, and injected fluidsused in enhanced oil recovery operations, e.g., steam floods, carbondioxide floods, caustic floods, micellar-polymer floods, and straightpolymer floods.

Referring now to the drawings, and in particular to FIG. 1, the presentinvention is illustrated by a flow chart. The flow chart illustrates anapparatus, method, and system of reservoir interrogation. The apparatus,method, and system of reservoir interrogation are designated generallyby the reference numeral 100.

In step 1 a tracer is provided. Step 1 is designated by the referencenumeral 102 in the flow chart of FIG. 1. The tracer is a tracer that canbe used in all applications that currently use conventional tracertechniques. In one embodiment the tracer is a standard tracers such asfluorescein disodium hydrate and 2,6-napthalein disulfonic acid sodiumsalt. The appearance of the tracer and the concentration is commonlymeasured using HPLC with a fluorescence detector. In various embodimentsof the invention multiple tracers are used, each contained in capsulesthat release the tracer after contact with specific conditions or thecapsule is recovered with the capsule intact and the analyzed. In thisway, reservoir conditions can be more accurately determined.

The tracer is encapsulating in a receptacle in step 2. Step 2 isdesignated by the reference numeral 104 in the flow chart of FIG. 1.Additional description and information will be described subsequently,particularly in connection with FIG. 2.

In step 3 the receptacle containing the tracer is injected into thereservoir. Step 3 is designated by the reference numeral 106 in the flowchart of FIG. 1.

In step 4 the tracer is analyzed for reservoir interrogation. Step 4 isdesignated by the reference numeral 108 in the flow chart of FIG. 1.

The present invention provides a reservoir interrogation apparatuscomprising a tracer encapsulated in a receptacle. Referring to FIG. 2,the tracer is shown encapsulating in a receptacle. The encapsulatedtracer is designated generally by the reference numeral 200. Theencapsulated tracer 200 includes a receptacle 202 and a tracer 204encapsulated within the receptacle 202. The tracer 204 can be a tracerthat can be used in all applications that currently use conventionaltracer techniques. This is a groundbreaking improvement in theinformation that can be obtained from tracer tests while preserving thestandard techniques and ease of use of existing tracer materials. No newinterrogation techniques would need to be developed. In addition, intactmicrocapsules could be collected and the interior liquid analyzed forreaction products or other changes as a result of exposure to elevatedtemperatures or other conditions.

Capsule Making

The present invention provides a method to make capsules and capsuleswithin capsules. A round injection tube that tapers to some opening,typically with an opening diameter from 1-1000 micrometers (□m), isinserted and secured into a square outer tube wherein the outer diameter(OD) of the round tube, which is typically 0.8-1.5 millimeters (mm), isslightly smaller than the inner diameter (ID) of the square outer tubein order to center the round injection tube within the square outertube. A round collection tube with an opening diameter typically 2-10times larger than the opening of the injection tube and an OD equivalentto the injection tube is inserted into the opposite end of the squareouter tube typically to within 100-800 □m of the injection tube andsecured in place. Liquid-tight connections are made to deliver the inner(core) fluid to the injection tube, the middle (shell) fluid to theinterstitial space between the round injection tube and the square outertube, and the outer (collection) fluid to the interstitial space betweenthe round collection tube and the square outer tube. Each fluid isdelivered with a controlled volumetric flow rate where flows for themiddle and outer fluids are typically 10-1000 times the inner fluid flowrate with typical flow rates on the order of 100-1000 μl/h. Inoperation, the inner fluid 708 with a viscosity of 1-1000 (cP) flows inthe injection tube. As the inner fluid proceeds down the channel itpasses through the tapered injection tube which is a droplet formingnozzle. The formed droplet is released from the nozzle and becomesencased in a spherical shell of the middle fluid 7; which has aviscosity of 10-100 times that of the inner fluid. The inner fluiddroplet becomes encased in the middle fluid forming an encapsulatedmicrocapsule that has a core with a thin outer shell. The outer fluid,with a viscosity of 10-100 times the inner fluid, flows in the outertube and hydro dynamically flow focuses to sever and form themicrocapsules at the active zone between the injection tube opening anddownstream up to several millimeters within the collection tube. Thisouter fluid carries the microcapsules into a collection container. Themicrocapsules can range from approximately 10-1000's μm in diameter withshell thicknesses that range from approximately 5-25% of the capsulediameter. Both the diameter and the shell thickness are tunable bychanging the microfluidic geometry or the fluid viscosities and flowrates.

The shell may be treated so that it undergoes a liquid to solidtransition via routes such as photocrosslinking and interfacialpolymerization. In addition, multiple devices may be stacked in sequenceor multiple devices may be fed into a single device so that capsuleswithin capsules may be formed with different inner fluids containedwithin each capsule while also controlling the number of capsules withina larger capsule.

Systems for producing microcapsules are described in U.S. Pat. No.7,776,927 and in U.S. Published Patent Application Nos. 2009/0012187 and2009/0131543 which are incorporated herein by reference. U.S. Pat. No.7,776,927 to Liang-Yin Chu et al., assigned to the President and Fellowsof Harvard College, discloses emulsions and the production of emulsions,including multiple emulsions and microfluidic systems for producingmultiple emulsions. A multiple emulsion generally describes largerdroplets that contain one or more smaller droplets therein which, insome cases, can contain even smaller droplets therein, etc. Emulsions,including multiple emulsions, can be formed in certain embodiments withgenerally precise repeatability, and can be tailored to include anynumber of inner droplets, in any desired nesting arrangement, within asingle outer droplet. In addition, in some aspects of the invention, oneor more droplets may be controllably released from a surroundingdroplet. U.S. Published Patent Application No. 2009/0012187 to Liang-YinChu et al, assigned to the President and Fellows of Harvard College,discloses multiple emulsions, and to methods and apparatuses for makingemulsions, and techniques for using the same. A multiple emulsiongenerally describes larger droplets that contain one or more smallerdroplets therein which, in some cases, can contain even smaller dropletstherein, etc. Emulsions, including multiple emulsions, can be formed incertain embodiments with generally precise repeatability, and can betailored to include any number of inner droplets, in any desired nestingarrangement, within a single outer droplet. In addition, in some aspectsof the invention, one or more droplets may be controllably released froma surrounding droplet. U.S. Published Patent Application No.2009/0131543 to David A. Weitz discloses multiple emulsions, and tomethods and apparatuses for making multiple emulsions. A multipleemulsion, as used herein, describes larger droplets that contain one ormore smaller droplets therein. The larger droplet or droplets may besuspended in a third fluid in some cases. In certain embodiments,emulsion degrees of nesting within the multiple emulsion are possible.For example, an emulsion may contain droplets containing smallerdroplets therein, where at least some of the smaller droplets containeven smaller droplets therein, etc. Multiple emulsions can be useful forencapsulating species such as pharmaceutical agents, cells, chemicals,or the like. In some cases, one or more of the droplets (e.g., an innerdroplet and/or an outer droplet) can change form, for instance, tobecome solidified to form a microcapsule, a liposome, a polymerosome, ora colloidosome. As described below, multiple emulsions can be formed inone step in certain embodiments, with generally precise repeatability,and can be tailored to include one, two, three, or more inner dropletswithin a single outer droplet (which droplets may all be nested in somecases). As used herein; the term “fluid”, generally means a material ina liquid or gaseous state. Fluids, however, may also contain solids,such as suspended or colloidal particles. U.S. Pat. No. 7,776,927 andU.S. Published Patent Application Nos. 2009/0012187 and 2009/0131543 areincorporated herein by this reference.

The present invention provides benefits in fabrication andmanufacturability. The beads can be fabricated at a size small enoughfor efficient mass transfer and large enough for ease of handling. Thepresent invention provides methods to fabricate liquid filled shells inthe size range of 100 microns to 1 mm with wall thickness from 5-10microns. The present invention provides benefits in survivability androbustness. The present invention identifies several polymers that canwithstand typical regeneration temperatures of 100-150 C. In addition,the selected polymers will be capable of withstanding small volumetricchanges due to absorption desorption of water.

Microcapsules

The encapsulated tracer 200 in some embodiments can be a microcapsule ormicrocapsules. The microcapsules will be made of different materials anddifferent wall thicknesses to achieve the desired result. This is, forinstance, dissolution of the capsule and release of the tracer afterimmediate exposure to a temperature (or fluid composition) of interestfollowed by release of a second, or third tracer after prolongedexposure to the same release trigger. In this way, tracers can bedesigned to specifically interrogate for the property of interest In oneembodiment; liquid-filled microcapsules are made with very thin polymershells. This invention specifically deals with the combination of thecontents of the capsules, which will be the typical tracer chemicalpreviously described or new reactant mixtures, with the shell materialsand geometry. These shells can be any number of polymer or othermaterials which are designed to dissolve, erode, or otherwise degradeunder specific environmental conditions such as elevated temperature orspecific chemical exposure.

Applicants use existing microfluidic assembly techniques as a platformfor creating droplets that contain a given tracer or other reactantmixture polymer skin which can dissolve or erode as desired releasingthe tracer. Additionally, the shell can be designed to stay completelyintact if desired. The fabrication technology allows Applicants tocontrol the size and skin thickness, and polydispersity of the capsules.Typically, once the droplets form, the applicants cure and the shellmaterial to form a solid shell via UV photopolymerization; however othermeans of curing such as interfacial polymerization and thermal treatmentare possible. The polymer surface layer 202 can be made of any ofseveral families of polymerizable or crosslink-able materials, includingsilicones and siloxanes such as polydimethylsiloxane, polymers such aspolyimides, polyamides, polyacrylates, polyurethanes, and adhesives suchas epoxies and mercapto-esters, and other materials.

The present invention will be further explained, illustrated, anddescribed in the following examples of systems of the present invention.The examples demonstrate the utility and/or function of the inventionhelp provide a full describe of the invention. The technological fieldwill dictate the relative importance of inclusion of examples in apatent application.

EXAMPLE 1

Referring now to FIG. 3, one example of the present invention isillustrated by a flow chart. The flow chart illustrates an apparatus,method, and system of reservoir interrogation. The apparatus, method,and system of reservoir interrogation are designated generally by thereference numeral 300.

In step 1 a tracer is provided. Step 1 is designated by the referencenumeral 302 in the flow chart of FIG. 3. The tracer is a tracer that canbe used in all applications that currently use conventional tracertechniques. In one embodiment the tracer is a standard tracers such asfluorescein disodium hydrate and 2,6-napthalein disulfonic acid sodiumsalt. The appearance of the tracer and the concentration is commonlymeasured using HPLC with a fluorescence detector. In various embodimentsof the invention multiple tracers are used, each contained inreceptacles that release the tracer after contact with specificconditions or the receptacle is recovered with the receptacle intact andthe analyzed. In this way, reservoir conditions can be more accuratelydetermined.

The tracer is encapsulating in a receptacle in step 2. Step 2 isdesignated by the reference numeral 304 in the flow chart of FIG. 3. Thereceptacle can be made of different materials and different wallthicknesses to achieve the desired result. For instance, dissolution ofthe receptacle and release of the tracer after exposure to apre-determined temperature or fluid composition or pressure receptaclecan be accomplished by dissolution of the receptacle and release of thetracer after exposure to a pre-determined temperature or fluidcomposition or pressure. The combination of the contents of thereceptacles, which will be the typical tracer chemical previouslydescribed or new reactant mixtures, with the shell materials andgeometry. These shells can be any number of polymer or other materialswhich are designed to dissolve, erode, or otherwise degrade underspecific environmental conditions such as elevated temperature orspecific chemical exposure.

In step 3 the receptacle containing the tracer is injected into thereservoir. Step 3 is designated by the reference numeral 306 in the flowchart of FIG. 3. The receptacle changes chemical constituent or color orfluorescence at a predetermined condition. For example, the tracer canbe released from the receptacle in the reservoir upon pre-determinedconditions and an analysis made regarding the collected tracer materialfor reservoir interrogation.

In step 4 the tracer is analyzed for reservoir interrogation. Step 4 isdesignated by the reference numeral 308 in the flow chart of FIG. 3. Forexample, the tracer can be analyzed for reservoir interrogation usingtests that are a standard method for obtaining information about theinterconnectedness of individual wells, pathways, sweep efficiency,reservoir storage volume, and the types of fluid at depth (through theuse of tracers that have distinct distribution coefficients).Subterranean fluids whose movements are capable of being monitored bythese tracers include, but are not limited to, geothermal brine, crudeoil, ground water, hazardous waste, and injected fluids used in enhancedoil recovery operations, e.g., steam floods, carbon dioxide floods,caustic floods, micellar-polymer floods, and straight polymer floods.

EXAMPLE 2

Referring now to FIG. 4, another example of the present invention isillustrated by a flow chart. The flow chart illustrates an apparatus,method, and system of reservoir interrogation. The apparatus, method,and system of reservoir interrogation are designated generally by thereference numeral 400.

In step 1 a tracer is provided. Step 1 is designated by the referencenumeral 402 in the flow chart of FIG. 4. The tracer is a tracer that canbe analyzed for reservoir interrogation after being encapsulated in areceptacle and the receptacle being injected into the reservoir andrecovered. In various embodiments of the invention multiple tracers areused, each contained in receptacles that are recovered with thereceptacles intact and the tracer analyzed. In this way, reservoirconditions can be more accurately determined.

The tracer is encapsulating in a receptacle in step 2. Step 2 isdesignated by the reference numeral 404 in the flow chart of FIG. 4. Thereceptacle can be made of different materials and different wallthicknesses to achieve the desired result. The combination of thecontents of the receptacle with the pre-determined shell materials andgeometry. These shells can be any number of polymer or other materials.

In step 3 the receptacle containing the tracer is injected into thereservoir. Step 3 is designated by the reference numeral 406 in the flowchart of FIG. 4. The receptacle changes chemical constituent or color orfluorescence upon encountering predetermined conditions. For example,the tracer within the receptacle travels into the reservoir andencounters the pre-determined conditions. The receptacle is recoveredintact and analysis made of the tracer material for reservoirinterrogation.

In step 4 the receptacle is recovered intact and the tracer material isanalyzed for reservoir interrogation. Step 4 is designated by thereference numeral 408 in the flow chart of FIG. 4. For example, thetracer can be analyzed for reservoir interrogation and obtaininginformation about the interconnectedness of individual wells, pathways,sweep efficiency, reservoir storage volume, and the types of fluid atdepth (through the use of tracers that have distinct distributioncoefficients). Subterranean fluids whose movements are capable of beingmonitored by these tracers include, but are not limited to, geothermalbrine, crude oil, ground water, hazardous waste, and injected fluidsused in enhanced oil recovery operations, e.g., steam floods, carbondioxide floods, caustic floods, micellar-polymer floods, and straightpolymer floods.

EXAMPLE 3

Referring now to FIGS. 5A and 5B, an example of a system of the presentinvention is illustrated. The system is designated by the referencenumeral 500. As shown in FIG. 5A, a well 502 is illustrated extendinginto the earth 504 and into a formation 506 penetrated by the well 502.The well 502 is shown having a borehole 508 extending into the earth 504and into the formation 506. The well 502 is shown with a casing 510. Thewell 502 extends into a reservoir 516.

The system 500 provides a method of interrogation of the reservoir 516.A tracer 512 is encapsulated providing a microencapsulation tracer 514.The microencapsulation tracer 514 is injected into the well 502 that islined by the casing 510 and continues until it is injected into thereservoir 516 as indicated by the arrows 518. The reservoir 516 isformed in the formation 506 and is defined by the boundary 520.

The microencapsulated tracer 512 will be released from the microcapsule514 when it comes into contact with fluids of a predeterminedtemperature or a predetermined chemistry⁻or a predetermined time. Themicrocapsule 514 containing the tracer 512 is shown being injected intothe reservoir 516 by the arrow 518. The tracer 512 is shown near theboundary 520 of the reservoir 516 after having been released when itcomes into contact with fluids of a predetermined temperature, apredetermined chemistry, or a predetermined time, or a predeterminedpressure, etc.

The microencapsulated tracer 114 includes a shell having a reactant inthe shell that changes at a predetermined temperature range, pressure,or other predetermined condition. The combination of the contents of themicroencapsulated tracer 114, which can be a prior art tracer chemicalor new reactant mixtures with shell materials and geometry. These shellscan be any number of polymer or other materials which are designed todissolve, erode, or otherwise degrade under specific environmentalconditions such as elevated temperature or specific chemical exposure.Wall thickness on these shells can be controlled via the fabricationprocess and typically can range from −10-100 um for overall capsulediameters of −50-500 um.

Applicants have used existing microfluidic assembly techniques as aplatform for creating droplets that contain a given tracer or otherreactant mixture polymer skin which can dissolve or erode as desiredreleasing the tracer. The fabrication technology allows Applicants tocontrol the size and skin thickness, and polydispersity of the capsules.Typically, once the droplets of the tracer form. Applicants cure andpolymer shell via UV photopolymerization; however other means of curingsuch as interfacial polymerization and thermal treatment are possible.

In the production of petroleum or minerals from subterranean formationsone must be knowledgeable about the formation. Tracers are used in suchreservoir engineering. The present invention provides tracers that arecontained in microcapsules. The microencapsulation of tracers relies onthe ability to contain the tracer, inject the tracer into a geologicformation as part of a standard tracer test, and recover the tracer onceit is released from the capsule. By preparing capsules of theappropriate material and wall thickness, the tracer will only bereleased when it comes into contact with fluids of the appropriatetemperature, chemistry, or time.

Tracers tests are a standard method for obtaining information about theinterconnectedness of individual wells, pathways, sweep efficiency,reservoir storage volume, and the types of fluid at depth (through theuse of tracers that have distinct distribution coefficients). Themicroencapsulated tracers of the present invention will enable thecollection of valuable additional information such as temperature,pressure, and fluid composition. A significant advantage of the proposedtechnique over other developing SMART tracer technologies is that theproposed technique uses standard tracers that are relatively easy to useand interpret. Fluid pumped from a production well can be analyzed inthe standard way. The user will look for breakthrough, the firstoccurrence of the tracer, to determine if the microencapsulated tracerhas been released, and if it has, the interpretation is that the releasewas triggered by the design of the capsule. The intent The intent is tocreate suites of tracers that have different responses to the reservoir.For instance, the appearance in production fluid of a tracerencapsulated so that the tracer is released at a specific temperaturewill inform the operator that parts of the reservoir exceed the releasetemperature. Suites of encapsulated tracers designed to release thetracer at distinct conditions of interest can provide a more completepicture of reservoir conditions in this manner.

The present invention utilizes standard tracers such as fluoresceindisodium hydrate and 2,6-napthalein disulfonic acid sodium salt. Theappearance of tracers, and the concentration is commonly measured usingHPLC with a fluorescence detector. Any standard tracer can be used. Indifferent embodiments, the invention uses multiple tracers, eachcontained in microcapsules that release the tracer after contact withspecific conditions. In this way, reservoir conditions can be moreaccurately determined.

The microcapsules will be made of different materials and different wallthicknesses to achieve the desired result. This is, for instance,dissolution of the capsule and release of the tracer after immediateexposure to a temperature (or fluid composition) of interest followed byrelease of a second, or third tracer after prolonged exposure to thesame release trigger. In this way, tracers can be designed tospecifically interrogate for the property of interest. This is agroundbreaking improvement in the information that can be obtained fromtracer tests while preserving the standard techniques and ease of use ofexisting tracer materials. No new interrogation techniques would need tobe developed. In addition, intact microcapsules could be collect and theinterior liquid analyzed for reaction products or other changes as aresult of exposure to elevated temperatures or other

FIG. 5B is the enlarge section of FIG. 5A providing more details of thereservoir 516. As shown in FIG. 5B, the system 500 provides a method ofinterrogation of the reservoir 516. A tracer 512 is encapsulatedproviding a microencapsulation tracer 514. The microencapsulation tracer514 is injected into the reservoir 516 as defined by the boundary 520.The microencapsulated tracer 512 is shown released from the microcapsule514 after it has come into contact with fluids of a predeterminedtemperature or a predetermined pressure or a predetermined chemistry ora predetermined time or other predetermined conditions.

In the production of petroleum or minerals from subterranean formationstracers are used in reservoir interrogation. The present inventionprovides tracers that are contained in microcapsules. Themicroencapsulation of tracers relies on the ability to contain thetracer, inject the tracer into a geologic formation as part of astandard tracer test, and recover the tracer once it is released fromthe capsule. By preparing capsules of the appropriate material and wallthickness, the tracer will only be released when it comes into contactwith fluids of the appropriate temperature, chemistry, or time.

The microcapsules 514 are made of different materials and different wallthicknesses to achieve the desired result. This is, for instance,dissolution of the capsule and release of the tracer after immediateexposure to a temperature (or fluid composition) of interest followed byrelease of a second, or third tracer after prolonged exposure to thesame release trigger. In this way, tracers can be designed tospecifically interrogate for the property of interest. This is agroundbreaking improvement in the information that can be obtained fromtracer tests while preserving the standard techniques and ease of use ofexisting tracer materials. No new interrogation techniques would need tobe developed. In addition, intact microcapsules could be collect and theinterior liquid analyzed for reaction products or other changes as aresult of exposure to elevated temperatures or other conditions.

EXAMPLE 4

Referring now to FIGS. 6, 7, and 8 an example of a system of the presentinvention is illustrated. The system is designated by the referencenumeral 600. An injection well 602 is shown extending into the earth 604and into a formation 606 penetrated by the well 602. The injection well602 is shown having a borehole 608 extending into the earth 604 and intothe formation 606. The injection well 602 is shown with a casing 610.The injection well 602 extends into a reservoir 616.

The system 600 provides a method of interrogation of the reservoir 616.A tracer 612 is encapsulated providing a microencapsulation tracer 614.The microencapsulated tracer 614 is fed into the injection well 602 thatis lined by the casing 610 and continues into the reservoir 616 asindicated by the arrows 618. The reservoir 616 is formed in theformation 606 and is defined by the boundary 626. The microencapsulatedtracer 614 will come into contact with fluids in the reservoir 616having a predetermined condition or conditions. The microencapsulatedtracer 614 is drawn into the recovery well 618 that is lined by thecasing 620 and continues to the analysis unit 624 as indicated by thearrows 618. The analysis unit 624 will be described in greater detailsubsequently.

The tracer material 612 in microencapsulated tracer 614 will have achange in characteristics when it comes into contact with fluids havinga predetermined condition or conditions and effectively record thepredetermined condition or conditions. The microcapsules are made ofdifferent materials and different wall thicknesses to achieve thedesired result. This is, for instance, to record exposure to atemperature or fluid characteristic of interest. In this way the tracer612 can be designed to specifically interrogate for the property ofinterest. The intact microencapsulated tracer 614 is collected throughthe recovery well 618 and the interior material analyzed for reactionproducts or other changes as a result of exposure to elevatedtemperatures or other conditions in the reservoir 616.

Referring now to FIG. 7, a flow chart illustrate illustrates analysis ofthe tracer for reservoir interrogation. The analysis of the tracer forreservoir interrogation is designated generally by the reference numeral700.

The microencapsulated tracer is drawn into the recovery well andcontinues to the analysis unit. The microencapsulated tracer isrecovered intact as illustrated by the box 702.

The arrow 704 illustrates that the microencapsulated tracer isinterrogated. The chemical constituent, color, fluorescence, or otherproperty of the tracer material in the encapsulated trace has beenaltered, activated, and/or modified as it passes through specifictemperature ranges, pressure ranges, chemical condition and/or otherconditions in the reservoir. The tracer material in themicroencapsulated tracer is interrogated as illustrated by the box 706.The tracer material is interrogated (optically, chemically, etc.) todetermine the conditions to which they were exposed.

The arrow 708 illustrates that data from interrogation of the materialin the tracer is analyzed. The analysis includes, but is not limited to,analysis for geothermal brine, crude oil, ground water, hazardous waste,and injected fluids used in enhanced oil recovery operations, e.g.,steam floods, carbon dioxide floods, caustic floods, micellar-polymerfloods, and straight polymer floods.

Referring now to FIG. 8, a flow chart illustrate illustrates theencapsulation of the tracer material. The encapsulation is designatedgenerally by the reference numeral 800. The tracer material is selectedas indicated by the box 802. The tracer material may be a typical tracerchemical or a new reactant mixture. The tracer material is selected tobe a material whose chemical constituent, color, fluorescence, or otherproperty will be altered, activated, and/or modified as it passesthrough specific temperature ranges, pressure ranges, chemical conditionand/or other conditions in the reservoir. This includes a material whosechemical constituent, color, fluorescence, or other property will bealtered, activated, and/or modified by the fluid of a geothermal brine,crude oil, ground water, hazardous waste, and injected fluids used inenhanced oil recovery operations, e.g., steam floods, carbon dioxidefloods, caustic floods, micellar-polymer floods, and straight polymerfloods.

Once the tracer material has been selected the encapsulation materialneeds to be selected as indicated by the arrow 804. The encapsulationmaterial is selected as indicated by the box 806. The encapsulationmaterial in some embodiments can be a material suitable for creatingmicrocapsules. The microcapsules will be made of different materials anddifferent wall thicknesses to achieve the desired result. In oneembodiment, liquid-filled microcapsules are made with very thin polymershells. The shells can be any number of polymer or other materials thatwill withstand specific environmental conditions such as elevatedtemperature or specific chemical exposure. Wall thickness on theseshells can be controlled via the fabrication process and typically canrange from −10-100 um for overall capsule diameters of −50-500 um.

Once the encapsulation material has been selected the encapsulation ofthe tracer material in the encapsulation material needs to be completedas indicated by the arrow 808. The encapsulation of the tracer materialin the encapsulation material is indicated by the box 806. Applicantsuse existing microfluidic assembly techniques as a platform for creatingdroplets that contain a given tracer or other reactant mixture polymerskin which will stay completely intact. The fabrication technologyallows Applicants to control the size and skin thickness, andpolydispersity of the capsules. Typically, once the droplets form.Applicants cure and polymer shell via UV photopolymerization; howeverother means of curing such as interfacial polymerization and thermaltreatment are possible. The polymer surface layer can be made of any ofseveral families of polymers, including polystyrene, polyethylene,polypropylene, nylon, and others.

EXAMPLE 5

Referring now to FIG. 9, another example of the present invention isillustrated by a flow chart. The flow chart illustrates an apparatus,method, and system of reservoir interrogation. The apparatus, method,and system of reservoir interrogation are designated generally by thereference numeral 900.

In step 1 a tracer is provided. Step 1 is designated by the referencenumeral 902 in the flow chart of FIG. 9. The tracer is a tracer that canbe used in all applications that currently use conventional tracertechniques. In one embodiment the tracer is a standard tracers such asfluorescein disodium hydrate and 2,6-napthalein disulfonic acid sodiumsalt. The appearance of the tracer and the concentration is commonlymeasured using HPLC with a fluorescence detector. In various embodimentsof the invention multiple tracers are used, each contained in capsulesthat release the tracer after contact with specific conditions or thecapsule is recovered with the capsule intact and the analyzed. In thisway, reservoir conditions can be more accurately determined.

The tracer is encapsulating in a receptacle in step 2. Step 2 isdesignated by the reference numeral 904 in the flow chart of FIG. 9. Thereceptacle can be made of different materials and different wallthicknesses to achieve the desired result. The receptacle is designed torelease the tracer after a pre-determined time. The receptacle shell canbe any number of polymer or other materials which are designed todissolve, erode, or otherwise degrade after a specific time.

In step 3 the receptacle containing the tracer is injected into thereservoir. Step 3 is designated by the reference numeral 906 in the flowchart of FIG. 9.

In step 4 the receptacle releases the tracer after the predeterminedtime. Step 4 is designated by the reference numeral 908 in the flowchart of FIG. 9.

In step 5 the tracer is recovered and analyzed for reservoirinterrogation. Step 5 is designated by the reference numeral 910 in theflow chart of FIG. 9. For example, the tracer can be analyzed forreservoir interrogation using tests that are a standard method forobtaining information about the interconnectedness of individual wells,pathways, sweep efficiency, reservoir storage volume, and the types offluid at depth (through the use of tracers that have distinctdistribution coefficients). Subterranean fluids whose movements arecapable of being monitored by these tracers include, but are not limitedto, geothermal brine, crude oil, ground water, hazardous waste, andinjected fluids used in enhanced oil recovery operations, e.g., steamfloods, carbon dioxide floods, caustic floods, micellar-polymer floods,and straight polymer floods.

EXAMPLE 6

Referring now to FIG. 10, another example of the present invention isillustrated by a flow chart. The flow chart illustrates an apparatus,method, and system of reservoir interrogation. The apparatus, method,and system of reservoir interrogation are designated generally by thereference numeral 1000.

In step 1 a tracer is provided. Step 1 is designated by the referencenumeral 1002 in the flow chart of FIG. 10. The tracer is a tracer thatcan be used in all applications that currently use conventional tracertechniques. In one embodiment the tracer is a standard tracers such asfluorescein disodium hydrate and 2,6-napthalein disulfonic acid sodiumsalt. The appearance of the tracer and the concentration is commonlymeasured using HPLC with a fluorescence detector. In various embodimentsof the invention multiple tracers are used, each contained in capsulesthat release the tracer after contact with specific conditions or thecapsule is recovered with the capsule intact and the analyzed. In thisway, reservoir conditions can be more accurately determined.

The tracer is encapsulating in a receptacle in step 2. Step 2 isdesignated by the reference numeral 1004 in the flow chart of FIG. 10.The receptacle can be made of different materials and different wallthicknesses to achieve the desired result. The receptacle is designed torelease the tracer after exposure to a pre-determined temperature. Thereceptacle shell can be any number of polymer or other materials whichare designed to dissolve, erode, or otherwise degrade under specificenvironmental conditions of temperature.

In step 3 the receptacle containing the tracer is injected into thereservoir. Step 3 is designated by the reference numeral 1006 in theflow chart of FIG. 10.

In step 4 the receptacle releases the tracer at the predeterminedtemperature. Step 4 is designated by the reference numeral 1008 in theflow chart of FIG. 10.

In step 5 the tracer is recovered and analyzed for reservoirinterrogation. Step 5 is designated by the reference numeral 1010 in theflow chart of FIG. 10. For example, the tracer can be analyzed forreservoir interrogation using tests that are a standard method forobtaining information about the interconnectedness of individual wells,pathways, sweep efficiency, reservoir storage volume, and the types offluid at depth (through the use of tracers that have distinctdistribution coefficients). Subterranean fluids whose movements arecapable of being monitored by these tracers include, but are not limitedto, geothermal brine, crude oil, ground water, hazardous waste, andinjected fluids used in enhanced oil recovery operations, e.g., steamfloods, carbon dioxide floods, caustic floods, micellar-polymer floods,and straight polymer floods.

EXAMPLE 7

Referring now to FIG. 11, another example of the present invention isillustrated flow chart. The flow chart illustrates an apparatus, method,and system of reservoir interrogation. The apparatus, method, and systemof reservoir interrogation are designated generally by the referencenumeral 1100.

In step 1 a tracer is provided. Step 1 is designated by the referencenumeral 1102 in the flow chart of FIG. 11. The tracer is a tracer thatcan be used in all applications that currently use conventional tracertechniques. In one embodiment the tracer is a standard tracers such asfluorescein disodium hydrate and 2,6-napthalein disulfonic acid sodiumsalt. The appearance of the tracer and the concentration is commonlymeasured using HPLC with a fluorescence detector. In various embodimentsof the invention multiple tracers are used, each contained in capsulesthat release the tracer after contact with specific conditions or thecapsule is recovered with the capsule intact and the analyzed. In thisway, reservoir conditions can be more accurately determined.

The tracer is encapsulating in a receptacle in step 2. Step 2 isdesignated by the reference numeral 1104 in the flow chart of FIG. 11.The receptacle can be made of different materials and different wallthicknesses to achieve the desired result. The receptacle is designed torelease the tracer after exposure to a pre-determined pressure. Thereceptacle shell can be any number of polymer or other materials whichare designed to dissolve, erode, or otherwise degrade under specificenvironmental conditions of pressure.

In step 3 the receptacle containing the tracer is injected into thereservoir. Step 3 is designated by the reference numeral 1106 in theflow chart of FIG. 11.

In step 4 the receptacle releases the tracer at the predeterminedpressure. Step 4 is designated by the reference numeral 1108 in the flowchart of FIG. 11.

In step 5 the tracer is recovered and analyzed for reservoirinterrogation. Step 5 is designated by the reference numeral 1110 in theflow chart of FIG. 11. For example, the tracer can be analyzed forreservoir interrogation using tests that are a standard method forobtaining information about the interconnectedness of individual wells,pathways, sweep efficiency, reservoir storage volume, and the types offluid at depth (through the use of tracers that have distinctdistribution coefficients). Subterranean fluids whose movements arecapable of being monitored by these tracers include, but are not limitedto, geothermal brine, crude oil, ground water, hazardous waste, andinjected fluids used in enhanced oil recovery operations, e.g., steamfloods, carbon dioxide floods, caustic floods, micellar-polymer floods,and straight polymer floods.

EXAMPLE 8

Referring now to FIG. 12, another example of the present invention isillustrated by a flow chart. The flow chart illustrates an apparatus,method, and system of reservoir interrogation. The apparatus, method,and system of reservoir interrogation are designated generally by thereference numeral 1200.

In step 1 a tracer is provided. Step 1 is designated by the referencenumeral 1202 in the flow chart of FIG. 12. The tracer is a tracer thatcan be used in all applications that currently use conventional tracertechniques. In one embodiment the tracer is a standard tracers such asfluorescein disodium hydrate and 2,6-napthalein disulfonic acid sodiumsalt. The appearance of the tracer and the concentration is commonlymeasured using HPLC with a fluorescence detector. In various embodimentsof the invention multiple tracers are used, each contained in capsulesthat release the tracer after contact with specific conditions or thecapsule is recovered with the capsule intact and the analyzed. In thisway, reservoir conditions can be more accurately determined.

The tracer is encapsulating in a receptacle in step 2. Step 2 isdesignated by the reference numeral 1204 in the flow chart of FIG. 12.The receptacle can be made of different materials and different wallthicknesses to achieve the desired result. The receptacle is designed torelease the tracer after exposure to a pre-determined chemical reaction.The receptacle shell can be any number of polymer or other materialswhich are designed to dissolve, erode, or otherwise degrade underspecific environmental conditions of chemical reaction.

In step 3 the receptacle containing the tracer is injected into thereservoir. Step 3 is designated by the reference numeral 1206 in theflow chart of FIG. 12.

In step 4 the receptacle releases the tracer at the predeterminedchemical reaction. Step 4 is designated by the reference numeral 1208 inthe flow chart of FIG. 12.

In step 5 the tracer is recovered and analyzed for reservoirinterrogation. Step 5 is designated by the reference numeral 1210 in theflow chart of FIG. 12. For example, the tracer can be analyzed forreservoir interrogation using tests that are a standard method forobtaining information about the interconnectedness of individual wells,pathways, sweep efficiency, reservoir storage volume, and the types offluid at depth (through the use of tracers that have distinctdistribution coefficients). Subterranean fluids whose movements arecapable of being monitored by these tracers include, but are not limitedto, geothermal brine, crude oil, ground water, hazardous waste, andinjected fluids used in enhanced oil recovery operations, e.g., steamfloods, carbon dioxide floods, caustic floods, micellar-polymer floods,and straight polymer floods.

EXAMPLE 9 Hazardous Waste

In an additional version of the invention, the source of a hazardouswaste is identified. For example, a hazardous waste can appear, amongother places, in a subterranean potable water source or in the basementof a building. There may be two or more operators proximate thecontaminated area handling the same hazardous waste. To determine whichoperator is responsible for the pollution (as well as the source of thepollution), a different tracer is incorporated into each of theoperators' wastes.

The present invention provides a method of reservoir interrogationincluding the steps of microencapsulation of a tracer so that themicroencapsulated tracer will be released when it comes into contactwith fluids of a predetermined temperature or a predetermined chemistryor a predetermined time; injecting the microencapsulated tracer into ageologic formation; and recovering the tracer once it is released. Inone embodiment the method of reservoir interrogation the step ofmicroencapsulation of a tracer so that the microencapsulated tracer willbe released when it comes into contact with fluids of a predeterminedtemperature, a predetermined chemistry, or a predetermined timecomprises microencapsulation of the tracer with a preselected materialor a preselected wall thickness so that the microencapsulated tracerwill be released when it comes into contact with fluids of apredetermined temperature, a predetermined chemistry, or a predeterminedtime. In another embodiment method of reservoir interrogation the stepof microencapsulation of a tracer so that the microencapsulated tracerwill be released when it comes into contact with fluids of apredetermined temperature, a predetermined chemistry, or a predeterminedtime comprises microencapsulation of the tracer with a shell having areactant in the shell that changes chemical constituent or color orfluorescence or other property at a predetermined temperature range or apredetermined condition; collecting the microencapsulation tracer; andinterrogating the microencapsulation tracer to determine the changes inchemical constituent or color or fluorescence or other property.

If a particular operator is handling the hazardous waste at more thanone location, it is preferable to incorporate a different tracer intoeach waste that is processed at a separate location. By periodicallyanalyzing samples from the polluted area, the operator and locationresponsible for the pollution can be identified and corrective actioncan then be commenced.

EXAMPLE 10 Steam Flood

Another exemplary process of the present invention entails monitoringthe fluids injected during a steam flood. In this version of theinvention, the steam is typically injected using a 5-spot or 9-spotinjection-producer pattern. Occasionally, early steam breakthroughoccurs at a producer well. To determine which of the injection wells ischanneling its injected fluid to the producer well, a different traceris added to each of the steam injection wells designed to service theaffected producer well. By analyzing samples of the produced fluids, theinjection well responsible for the early breakthrough is identifiableand, once identified, remedial action can be taken. The interrogationincludes the steps of microencapsulation of the tracer so that themicroencapsulated tracer will be released when it comes into contactwith fluids of a predetermined temperature or a predetermined chemistryor a predetermined time; injecting the microencapsulated tracer into ageologic formation; and recovering the tracer once it is released. Inone embodiment the method of reservoir interrogation the step ofmicroencapsulation of a tracer so that the microencapsulated tracer willbe released when it comes into contact with fluids of a predeterminedtemperature, a predetermined chemistry, or a predetermined timecomprises microencapsulation of the tracer with a preselected materialor a preselected wall thickness so that the microencapsulated tracerwill be released when it comes into contact with fluids of apredetermined temperature, a predetermined chemistry, or a predeterminedtime. In another embodiment method of reservoir interrogation the stepof microencapsulation of a tracer so that the microencapsulated tracerwill be released when it comes into contact with fluids of apredetermined temperature, a predetermined chemistry, or a predeterminedtime comprises microencapsulation of the tracer with a shell having areactant in the shell that changes chemical constituent or color orfluorescence or other property at a predetermined temperature range or apredetermined condition; collecting the microencapsulation tracer; andinterrogating the microencapsulation tracer to determine the changes inchemical constituent or color or fluorescence or other property.

EXAMPLE 11 Geothermal

A geothermal field will be used to illustrate one process of the presentinvention. A geothermal field usually comprises one or more productionwells for producing geothermal brine from one or more subterraneangeothermal reservoirs. Heat is extracted from the produced brine and theresulting modified brine is either injected into a subterraneanformation through one or more injection wells or disposed of in anothermanner. Occasionally, water or different brine is injected to rechargethe formation.

In order to determine whether the fluid injected into a specificinjection well is adversely affecting the produced geothermal brines(e.g., causing a cooling effect), a tracer is incorporated into thatinjected fluid and at least one brine sample from each of one or more ofthe production wells (and preferably from each of all of the productionwells) is periodically assayed for its presence.

The present invention provides a method of reservoir interrogationincluding the steps of microencapsulation of a tracer so that themicroencapsulated tracer will be released when it comes into contactwith fluids of a predetermined temperature or a predetermined chemistryor a predetermined time; injecting the microencapsulated tracer into ageologic formation; and recovering the tracer once it is released. Inone embodiment the method of reservoir interrogation the step ofmicroencapsulation of a tracer so that the microencapsulated tracer willbe released when it comes into contact with fluids of a predeterminedtemperature, a predetermined chemistry, or a predetermined timecomprises microencapsulation of the tracer with a preselected materialor a preselected wall thickness so that the microencapsulated tracerwill be released when it comes into contact with fluids of apredetermined temperature, a predetermined chemistry, or a predeterminedtime. In another embodiment method of reservoir interrogation the stepof microencapsulation of a tracer so that the microencapsulated tracerwill be released when it comes into contact with fluids of apredetermined temperature, a predetermined chemistry, or a predeterminedtime comprises microencapsulation of the tracer with a shell having areactant in the shell that changes chemical constituent or color orfluorescence or other property at a predetermined temperature range or apredetermined condition; collecting the microencapsulation tracer; andinterrogating the microencapsulation tracer to determine the changes inchemical constituent or color or fluorescence or other property.

To determine which of a plurality of injection wells is injecting fluidsadversely impacting brine produced from one or more production wells, adifferent tracer is incorporated into each of a plurality of fluidstreams injected into respective injection wells. In this version,samples of the brines produced from one or more of the production wells(preferably from each of the production wells) are also periodicallyanalyzed for the presence of these tracers. By judiciously selecting thetracers, a single analysis is used to check each sample for the presenceof all tracers employed in the monitoring program—thereby saving asignificant amount of analytical time, effort, and money.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A method of reservoir interrogation, comprising the steps of:encapsulating a tracer in a receptacle, injecting said tracerencapsulated in a receptacle into the reservoir, and analyzing saidtracer for reservoir interrogation.
 2. The method of reservoirinterrogation of claim 1 wherein said step of injecting said tracerencapsulated in a receptacle into the reservoir comprises injecting saidtracer encapsulated in a receptacle into the reservoir wherein saidtracer will be released from said receptacle upon encounteringpre-determined conditions and wherein said step of analyzing said tracerfor reservoir interrogation comprises collecting said tracer upon saidtracer being released from said receptacle after encountering saidpre-determined conditions and analyzing said collected tracer forreservoir interrogation.
 3. The method of reservoir interrogation ofclaim 2 wherein said step of said tracer being released uponencountering pre-determined conditions comprises said tracer beingreleased upon encountering a pre-determined condition of time,
 4. Themethod of reservoir interrogation of claim 2 wherein said step of saidtracer being released upon encountering pre-determined conditionscomprises said tracer being released upon encountering a pre-determinedcondition of temperature.
 5. The method of reservoir interrogation ofclaim 2 wherein said step of said tracer being released uponencountering pre-determined conditions comprises said tracer beingreleased upon encountering a pre-determined condition of chemistry. 6.The method of reservoir interrogation of claim 2 wherein said step ofsaid tracer being released upon encountering pre-determined conditionscomprises said tracer being released upon encountering a pre-determinedcondition of pressure.
 7. The method of reservoir interrogation of claim1 wherein said step of encapsulating a tracer in a receptacle comprisesmicroencapsulating a tracer in a receptacle so that saidmicroencapsulated tracer will be released from said receptacle when saidmicroencapsulated tracer comes into contact with fluids of apredetermined temperature, fluids of a predetermined chemistry, fluidsof a predetermined time or fluids of a predetermined pressure.
 8. Themethod of reservoir interrogation of claim 1 wherein said step ofanalyzing said tracer for reservoir interrogation comprises collectingsaid microencapsulation tracer wherein said receptacle remains intactand interrogating said microencapsulation tracer for reservoirinterrogation.
 9. The method of reservoir interrogation of claim 8wherein said step of interrogating said microencapsulation tracer forreservoir interrogation comprises interrogating said microencapsulationtracer for chemical constituent, color, fluorescence, or other propertyof said microencapsulation tracer.
 10. A method of reservoirinterrogation, comprising the steps of: encapsulating a tracer in areceptacle, injecting said tracer encapsulated in a receptacle into thereservoir wherein said tracer will be released from said receptacle uponencountering pre-determined conditions, and analyzing said tracer forreservoir interrogation by collecting said tracer upon said tracer beingreleased from said receptacle after encountering said pre-determinedconditions and analyzing said collected tracer for reservoirinterrogation.
 11. The method of reservoir interrogation of claim 10wherein said step of said tracer being released upon encounteringpre-determined conditions comprises said tracer being released uponencountering a pre-determined condition of time.
 12. The method ofreservoir interrogation of claim 10 wherein said step of said tracerbeing released upon encountering pre-determined conditions comprisessaid tracer being released upon encountering a pre-determined conditionof temperature.
 13. The method of reservoir interrogation of claim 10wherein said step of said tracer being released upon encounteringpre-determined conditions comprises said tracer being released uponencountering a pre-determined condition of pressure.
 14. The method ofreservoir interrogation of claim 10 wherein said step of said tracerbeing released upon encountering pre-determined conditions comprisessaid tracer being released upon encountering a pre-determined conditionof chemistry.
 15. The method of reservoir interrogation of claim 10wherein said step of encapsulating a tracer in a receptacle comprisesmicroencapsulating a tracer in a receptacle so that saidmicroencapsulated tracer will be released from said receptacle when saidmicroencapsulated tracer comes into contact with fluids of apredetermined temperature, fluids of a predetermined chemistry, fluidsof a predetermined time or fluids of a predetermined pressure.
 16. Anapparatus for reservoir interrogation wherein the reservoir has specifictemperature ranges or pressure ranges or chemical conditions,comprising: a tracer material whose chemical constituent or color orfluorescence will be altered or activated or modified when it encountersthe specific temperature ranges or pressure ranges or chemicalconditions in the reservoir, and a receptacle encapsulating said tracermaterial, said receptacle made of a material that will release saidtracer material when said receptacle encounters the specific temperatureranges or pressure ranges or chemical conditions in the reservoir. 17.The apparatus for reservoir interrogation of claim 16 wherein saidreceptacle encapsulating said tracer material is receptacle made of apolymer.
 18. The apparatus for reservoir interrogation of claim 16wherein said receptacle encapsulating said tracer material is receptaclemade of nylon.
 19. The apparatus for reservoir interrogation of claim 16wherein said tracer material is a standard tracer material.
 20. Theapparatus for reservoir interrogation of claim 16 wherein said tracermaterial is fluorescein disodium hydrate and 2,6-napthalein disulfonicacid sodium salt.
 21. The apparatus for reservoir interrogation of claim16 wherein said receptacle encapsulating said tracer material comprisesmultiple concentric shells.
 22. The apparatus for reservoirinterrogation of claim 16 further comprising at least one additional atracer material whose chemical constituent or color or fluorescence willbe altered or activated or modified when it encounters the specifictemperature ranges or pressure ranges or chemical conditions in thereservoir, and at least one additional receptacle encapsulating saidtracer material, said receptacle made of a material that will releasesaid tracer material when said receptacle encounters the specifictemperature ranges or pressure ranges or chemical conditions in thereservoir.
 23. An apparatus for reservoir interrogation, comprising: atracer material whose chemical constituent or color or fluorescence willbe altered or activated or modified as it passes through specifictemperature ranges or pressure ranges or chemical conditions in thereservoir, and a receptacle encapsulating said tracer material, saidreceptacle made of a material that will remain intact in the reservoir.24. The apparatus for reservoir interrogation of claim 23 wherein saidreceptacle encapsulating said tracer material is receptacle made of apolymer.
 25. The apparatus for reservoir interrogation of claim 23wherein said receptacle encapsulating said tracer material is receptaclemade of nylon.
 26. A method of making an apparatus for reservoirinterrogation wherein the reservoir has specific temperature ranges orpressure ranges or chemical conditions, comprising the step of:providing a tracer material whose chemical constituent or color orfluorescence will be altered or activated or modified when it encountersthe specific temperature ranges or pressure ranges or chemicalconditions in the reservoir, and encapsulating said tracer material in areceptacle, said receptacle made of a material that will release saidtracer material when said receptacle encounters the specific temperatureranges or pressure ranges or chemical conditions in the reservoir.